Weld backing

ABSTRACT

A reusable weld backing capable of withstanding long use, which is held against the underside of a workpiece to provide weld-metal support in full penetration welding, the weld backing comprising a substrate made from copper or a copper alloy; and a copper-aluminum alloy layer containing 9 to 23% by weight of aluminum and formed at least on the surface of the substrate, the surface being on the side which faces a weld zone.

TECHNICAL FIELD

The present invention relates to a weld backing that is held against theunderside of a workpiece to provide adequate weld-metal support in fullpenetration welding and more particularly, to a weld backing suited foruse with a movable backing positioning system.

BACKGROUND ART

In prior art full penetration welding using a backing material, thefollowing procedures are usually taken. Firstly, a weld backing isformed from copper or a copper alloy with its length being identical tothe length of the weld line of a workpiece to be welded and itsconfiguration fitting to the shape of the weld line. Such a weld backingis held against the underside of the weld zone where a groove is formedand is fixed in position being supported by a number of supportingmembers. In this condition, a welding machine is moved along the weldline to weld throughout the entire length of the weld line. Aftercompletion of welding, the weld backing as well as its supportingmembers are removed.

However, the conventional weld backing made from copper or a copperalloy suffers from the following disadvantages: (1) the weld backing istoo soft and therefore liable to wear; and (2) the penetration beadtends to stick to the weld backing in high temperature zones. For thesereasons, the conventional weld backing is not reusable and cannotwithstand long service. The present invention has been made in order toovercome such disadvantages and therefore an object of the invention isto provide a weld backing which is repeatedly usable in full penetrationwelding and can withstand long service.

DISCLOSURE OF THE INVENTION

The above and other objects can be achieved by a weld backing accordingto the invention which is held against the underside of a workpiece toprovide weld-metal support in full penetration welding, the weld backingcomprising: a substrate made from copper or a copper alloy; and acopper-aluminum alloy layer containing 9 to 23% by weight of aluminumand formed at least on the surface of the substrate, the surface beingon the side which faces a weld zone.

By forming the copper-aluminum alloy layer which contains 9 to 23% byweight of aluminum and is highly abrasion-resistant, on the substratemade from copper or a copper alloy, the abrasion resistance of thesurface of the weld backing can be highly improved. Further, since thecopper-aluminum alloy has bad affinity to a bead, the penetration beaddoes not stick to the surface of the weld backing and therefore thesmoothness of the backing surface can be ensured. These characteristicsenable the weld backing to be reused and to be used for a long period.

The copper-aluminum alloy layer contains 9 to 23% by weight of aluminum,for the reason that when the aluminum content is less than 9% by weight,satisfactory hardness cannot be obtained and when it exceeds 23% byweight, the weld backing becomes too brittle for practical use althoughthe hardness obtained is satisfactory. The preferable aluminum contentis in the range of 16 to 22% by weight. When the content falls in thisrange, the copper-aluminum alloy layer is not brittle but possesses highhardness. The hardness of the copper-aluminum alloy layer is preferably250 to 700 mHv in practice and its thickness is preferably 20 to 300 μm.

The weld backing may include a cooling means for cooling thecopper-aluminum alloy layer. By cooling the copper-aluminum alloy layerwith the cooling means, the solidification of a penetration beadmaintained by surface tension can be speeded up and the resistance toabrasion and adherence at the surface of the weld backing can bemarkedly improved. The cooling means may be a cooling medium that iscirculated or stored within an interior space of the weld backing.

In a preferable form, the weld backing is made from copper or a copperalloy, and the copper-aluminum alloy layer is formed on the substratemade from the copper or copper alloy, and the cooling medium serving asthe cooling means for cooling the copper-aluminum alloy layer iscirculated or stored within the interior space defined in the weldbacking. Further, the weld backing may be composed of a box-shaped bodyportion which is open at one end and closed at the other end so as toform a bottom; and a lid portion for closing the opening end of thebox-shaped body portion. At least such a lid portion is formed fromcopper or a copper alloy. The copper or copper alloy forming the lidportion serves as the substrate and the copper-aluminum alloy layer isformed on the surface of the copper or copper alloy. The interior spaceis defined by the box-shaped body portion and the lid portion and thecooling medium is circulated or stored in this space as the coolingmeans for cooling the copper-aluminum alloy layer.

The cooling medium such as cooling water circulating within the interiorspace may be introduced into the interior space through an inlet formedat one side of the interior space and let out through an outlet formedat the other side of the interior space. These inlet and outlet may beformed as to be offset from each other. Alternatively, the inlet andoutlet through which the cooling medium may be introduced and let outmay be formed at the same side with a weir between.

The weld backing may have a desired configuration as far as it conformsto the shape of a joint to be welded. For example, the weld backing maybe substantially pentagonal or circular in section.

Preferably, the copper-aluminum alloy layer is formed by applyingaluminum infiltration treatment to the surface of the substrate madefrom copper or a copper alloy. For instance, the copper-aluminum alloylayer may be formed in such a way that: after the substrate has been putin a half-closed vessel together with aluminum penetrant which contains(i) iron-aluminum alloy powder or aluminum power; (ii) alumina powder;and (iii) ammonium chloride powder serving as a penetration accelerator,the vessel is constantly heated to 500° to 750° C. for 5 to 15 hourswhile inert gas or reducing gas being introduced into the vessel.

The weld backing of the invention is preferably mounted on a movablebacking positioning system comprising:

(a) a wheeled carriage for movably towards the face of the workpiece,supporting the weld backing at the underside of the workpiece so as toface the weld backing to the workpiece, the carriage being movable alonga weld line of the workpiece;

(b) follower elements attached to the weld backing, which follow themovement along the underside of the workpiece, being in contact with theunderside of the workpiece all the time to maintain the gap between theunderside of the workpiece and the weld backing to be suitable forobtaining desired bead thickness; and

(c) energizing means such as resilient members for energizing the weldbacking such that the follower elements are always in contact with theunderside of the workpiece.

When the weld backing is mounted on such a movable backing positioningsystem, frequent replacement of the weld backing is no longer neededsince the weld backing has high resistance to abrasion and adherence,and therefore the operational efficiency of the movable backingpositioning system can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 are for explaining a preferred embodiment of the weldbacking of the invention;

FIG. 1 is an exploded perspective view of the weld backing;

FIG. 2 is a sectional view of the weld backing;

FIG. 3 is a graph showing the sectional composition of a copper-aluminumalloy layer obtained by the EPMA analysis.

FIG. 4 is a graph showing the hardness of the copper-aluminum alloylayer;

FIGS. 5 to 9 are for explaining a first example of the application ofthe weld backing of the invention to a movable backing positioningsystem;

FIG. 5 is a perspective view of the movable backing positioning system;

FIG. 6 is a side view of the movable backing positioning system;

FIG. 7 is a plan view of the movable backing positioning system;

FIG. 8 is a view of the movable backing positioning system as it is inoperation for full penetration welding;

FIG. 9 is a sectional view of the workpiece which has been welded;

FIG. 10 is a sectional view of a weld backing according to amodification;

FIGS. 11 to 13 are for explaining a second example of the application ofthe weld backing of the invention to a movable backing positioningsystem;

FIG. 11 is a perspective view of the movable backing positioning system;

FIG. 12 is a side view of the movable backing positioning system;

FIG. 13 is a rear elevation of the movable backing positioning system;

FIG. 14 is for explaining the structure of the weld backing of thesecond application example in detail;

FIG. 14(a) is a side elevation, partially in section, of the weldbacking;

FIG. 14(b) is a section of the weld backing shown in FIG. 14(a) takenalone line A--A of FIG. 14(a);

FIG. 15 is for explaining a modification of the weld backing of thesecond application example;

FIG. 15(a) is a side elevation, partially in section, of the weldbacking; and

FIG. 15(b) is a section of the weld backing shown in FIG. 15(a) takenalong line B--B of FIG. 15(a).

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the drawings, preferred embodiments of a weld backingaccording to the invention and examples of the application of the weldbacking to a movable backing positioning system will be hereinafterdescribed.

In FIGS. 1 and 2, there is shown a hollow, rectangular parallelepipedweld backing 11. The weld backing 11 is comprised of a backingbox-shaped body portion 11a which is open at the top and closed at thebottom and a backing lid portion 11b placed on the top of the backingbox-shaped body portion 11a so as to close the opening. The interiorspace of the backing box-shaped body portion 11a is a cooling waterchamber 12 that is communicated with a cooling water inlet 13a providedat the front part thereof and a cooling water outlet 13b provided at therear part thereof. These cooling water inlet 13a and cooling wateroutlet 13b are so positioned as to be offset from each other. Coolingwater is introduced into the interior of the cooling water chamber 12through the cooling water inlet 13a and expelled from the weld backing11 through the cooling water outlet 13b. With the circulation of coolingwater, the weld backing 11, especially the backing lid portion 11b iskept cool. On the top of the backing box-shaped body portion 11a isformed a ring groove 14 enclosing the opening. Six threaded holes 15 areformed outside the ring groove 14. At least the backing lid portion 11bincludes a substrate formed from a material having good heatconductivity such as copper or copper alloys (e.g., copper-chrome). Acopper-aluminum alloy layer 16 in which aluminum is diffused andinfiltrated is formed on at least the surface of the substrate facingthe weld zone, thereby improving the abrasion resistance and adherenceresistance of the weld backing 11. The backing lid portion 11b isinteriorly provided with a cooling water chamber 12a at the centerthereof, the contour of which is identical with that of the opening ofthe backing box-shaped body portion 11a. Outside the cooling waterchamber 12a are defined bolt holes 17 corresponding to the threadedholes 15. The weld backing 11 as described above is fabricated in thefollowing procedures: After a seal member 18 such as O-rings or gasketshas been fitted in the ring groove 14 of the backing box-shaped bodyportion 11a, the backing lid portion 11b is overlaid on the backingbox-shaped body portion 11a as indicated by an arrow in FIG. 1 so thatthe opening is closed. Then, flush head bolts 19 are inserted in thebolt holes 17 of the backing lid portion 11b and screwed into thethreaded holes 15 of the backing box-shaped body portion 11a.

Experience has shown by heating the copper-aluminum alloy containing 9to 23% by weight of aluminum to the proximity of 570° C., either the(α+γ₂) eutectoid phase, the γ₂ phase or the δ phase is obtained,depending on the ratio of aluminum contained in the alloy. (9 wt %≦Al<16wt %→the (α+γ₂) eutectoid phase; 16 wt %≦Al≦22 wt %→the γ₂ phase; and 22wt %<Al≦23 wt %→the γ₂ and δ phases). The α phase of copper aluminumalloys is soft, having a hardness of 100 mHv or less, while the hardnessof the γ₂ phase is 600 to 750 mHv. The hardness of the (α+}₂) eutectoidphase in which both the α phase and the γ phase exist is intermediatebetween these phases, i.e., 200 to 350 mHv, depending on the percentageof the γ₂ phase contained. Therefore, in case that the Al content isAl<9 wt %, the alloy layer after heating treatment has the soft α phaseas the matrix, which exhibits unsatisfactory abrasion resistance In casethat the Al content is Al>23 wt %, the alloy layer has only the brittleδ phase, and therefore the alloy layer is easily peeled off or droppedoff by a little shock. In view of the above facts, the aluminum contentof the copper-aluminum alloy layer 16 formed on the backing lid portion11b is most preferably in the range of 16 wt %≦Al≦22 wt with which onlythe γ₂ phase is formed. However, the (α+γ₂) eutectoid phase and the γ₂and δ phases are also acceptable, in which case, the Al content is inthe range of 9 wt %≦Al≦23 wt %.

In this embodiment, the copper-aluminum alloy layer 16 of the weldbacking 11 is formed in such a way that, after the backing lid portion11b has been put in a half-closed vessel (not shown) together with analuminum penetrant containing 30% by weight of aluminum powder; 69% byweight of alumina powder; and 1% by weight of ammonium chloride, thehalf-closed vessel is heated to 570° C. for 8 hours while argon gasbeing introduced into the vessel, so that the copper-aluminum alloylayer 16 is formed on the backing lid portion 11b formed from acopper-chrome alloy in this embodiment.

FIGS. 3 and 4 show the sectional composition analyzed by the EPMAanalysis and hardness of the copper-aluminum alloy layer 16. It isunderstood from FIGS. 3 and 4 that the copper-aluminum alloy layer 16 isformed on the surface of the backing lid portion 11b, with an aluminumconcentration of about 22 wt %, thickness of about 70 μm and hardness ofabout 680 mHv.

Although iron-aluminum alloy powder may be used as the aluminumpenetrant instead of aluminum powder and alumina powder when thecopper-aluminum alloy layer 16 is formed, the use of aluminum power andalumina powder is more preferable in view of the reaction speed and theconcentration of aluminum contained.

Now there will be given an explanation on cases where such a weldbacking 11 is mounted on a movable backing positioning system for fullpenetration welding, while making reference to the drawings.

Referring to FIGS. 5 to 9, a first application example will bedescribed. A movable backing positioning system 21 of the firstapplication example is suited for full penetration welding of abox-shaped workpiece 22 and includes a wheeled carriage 23 that is freeto move on the inner bottom wall of the workpiece 22 in a lateraldirection in FIGS. 6 and 7. The wheeled carriage 23 has four wheels 24at the under part thereof, and the front wheels 24 (located at the leftwhen viewing the drawings) are rotated by a DC servo motor 25 equippedwith reduction gears through a bevel gear 26. The back wheels 24 arecoupled by gears to a rotary encoder 27 that detects the rotation speedof the wheels 24. The rotary encoder 27 is used to control the travelspeed of the wheeled carriage 23 and to detect the welding position.

The front end and rear end of the wheeled carriage 23 are provided withbrackets 28 which are positioned at the right and left of each end. Thebrackets 28 at the front end project forwards while the brackets 28 atthe rear end project backwards. An arm 29 is screwed in each bracket 28,extending laterally with respect to the wheeled carriage 23. Attached tothe tip of each arm 29 is a guide roller 30 that is freely rotatable ina horizontal plane. These guide rollers 30 turn, moving along the sidewalls of the workpiece 22 when the wheeled carriage 23 moves forwardsand backwards, so that the position of the wheeled carriage 23 in alateral direction is restricted by the guide rollers 30. Two nuts 31 arefitted on each arm 29 so as to hold the bracket 28 between. By adjustingthe positions of the nuts 31 with respect to the arms 29, the extent towhich the arms 29 project laterally can be controlled.

Four threaded bars 32 are vertically threaded in an upper plate 23a ofthe wheeled carriage 23 at front part of the wheeled carriage 23. Thesethreaded bars 23 are also threaded in a supporting plate 33 that is aspecified distance apart from the top face of the upper plate 23a. Twopairs of nuts 34 are fitted on each threaded bar 32, such that the upperplate 23a and the supporting plate 33 are respectively tightened bythese pairs of nuts 34 from the top and underside. By adjusting thepositions of the nuts 34 with respect to the threaded bars 32, thespacing between the upper plate 23a and the supporting plate 33 of thewheeled carriage 23 can be controlled.

There is provided a backing retaining plate 35 that is positioned aboveand in parallel with the supporting plate 33. Fixedly attached to thetop face of the backing retaining plate 35 is the hollow, rectangularparallelepiped weld backing 11 as already described above. The backingretaining plate 35 is provided with projecting parts 36 which arepositioned at the front and rear parts of the backing retaining plate35, projecting laterally. There are four struts 37 each of which isfixed to each projecting part 36, projecting downwardly in a verticaldirection therefrom. Each of the struts 37 penetrates through each eyehole 38 defined in the supporting plate 33, extending downwards underthe supporting plate 33. The tip of each strut 37 is provided with aretaining ring 37a. There are provided four compression springs 39between the underside of the backing retaining plate 35 and the top faceof the supporting plate 33, each surrounding each of the struts 37. Theprovision of the compression springs 39 allow the weld backing 11 to beresiliently supported on the supporting plate 33.

An air cylinder 40 is attached to the underside of the backing retainingplate 35 so as to be positioned at the center of the weld backing 11.The air cylinder 40 has a cylinder rod 40a penetrating through an eyehole 41 defined in the supporting plate 33 to extend downwards under thesupporting plate 33. At the tip of the cylinder rod 40a, there isfixedly attached an engaging piece 42 that can be engaged with thesupporting plate 33. By operating the air cylinder 40 to draw thecylinder rod 40a, the engaging piece 42 is engaged with the underside ofthe supporting plate 33. This engagement allows the weld backing 11 tobe pulled towards the supporting plate 33, against the energizing forceof the compression springs 39.

Cylindrical follower element retainers 43 are screwed in the top face ofthe backing retaining plate 35 at the corners thereof. Each of thefollower element retainers 43 retains a follower element 44 at thecenter of the top face thereof. Each follower element 44 comprises aball caster and is positioned so as to project upwards slightly abovethe top face of the weld backing 11. The follower elements 44 turn beingin contact with the underside of the workpiece 22, so that a specifiedspacing can be kept between the weld backing 11 and the workpiece 22.The positions of the follower element retainers 43 in a verticaldirection (i.e., the spacing between the weld backing 11 and theworkpiece 22) can be controlled by adjusting the installation positionof the follower element retainers 43 with respect to the backingretaining plate 35.

There is provided a workpiece detection sensor 46 at one side of theweld backing 11. The workpiece detection sensor 46 comprises a proximityswitch attached to a rectangular plate 45 secured to the top of thebacking retaining plate 35. The workpiece detection sensor 46 detectsthe presence or absence of the workpiece 22 in order to control theoperation of the air cylinder 40. A detection piece 47 is attached tothe rear end of the backing retaining plate 35, extending downwards, anda photoelectric detector 48 in the form of a groove is supported at thesupporting plate 33, for detecting the detection piece 47. Thephotoelectric detector 48 detects the presence or absence of thedetection piece 47 in order to judge whether the weld backing 11 is atan upper position or lower position. At the rear part of the wheeledcarriage 23, a solenoid valve 49 for switching the operation of the aircylinder 40 and other control units are mounted and are covered with adust proof cover 50 (although the dust proof cover 50 is not shown inFIGS. 6 and 7).

Reference is now made to FIGS. 8 and 9, for explaining the operation ofthe movable backing positioning system 21 as described above, taking anexample in which full penetration welding is performed on the box-shapedworkpiece 22.

As the preparatory stage. the vertical position of the supporting plate33 in relation to the wheeled carriage 23 is adjusted such as to conformwith the spacing between the inner top wall and inner bottom wall of theworkpiece 22 by adjusting the positions of the threaded bars 32; thelateral positions of the arms 29 are adjusted such as to conform withthe spacing between the inner side walls of the workpiece 22 and suchthat the groove face S of the workpiece 22 is positioned above the weldbacking 11; and the installation positions of the follower elementretainers 43 are adjusted such that the spacing between the underside ofthe workpiece 22 and the top face of the weld backing 11 becomes equalto the thickness of a penetration bead RB.

After the preparation, while the air cylinder 40 is operated to pull theweld backing 11 towards the supporting plate 33, against the energizingforce of the compression springs 39, the wheeled carriage 23 is let inthe interior space of the box-shaped workpiece 22 by actuating the DCservo motor 25. At that time, the position of the wheeled carriage 23 ina lateral direction of FIG. 8 is restricted by the guide rollers 30disposed at the tip of the arms 29 and moving along the inner side wallsof the workpiece 22. Thus, the wheeled carriage 23 moves along the weldline of the workpiece 22. The travel speed of the wheeled carriage 23 iscontrolled by a control unit (not shown) based on the rotation speed ofthe wheels 24 detected by the rotary encoder 27.

After the wheeled carriage 23 has started to travel and the leading endof the workpiece 22 has been detected by the workpiece detection sensor46, a detection signal is released to the control unit so that the aircylinder 40 is operated to move the cylinder rod 40a forwards. Theforward movement of the cylinder rod 40a allows the engagement piece 42to be disengaged from the supporting plate 33, so that the weld backing11 is raised by the energizing force of the compression springs 39 untilthe follower elements 44 come in contact with the underside of theworkpiece 22. When the weld backing 11 accordingly reaches the upperposition, the photoelectric detector 48 becomes conductive and thusdetects that the weld backing 11 is in a normal position.

At this point, welding is started. A torch-like welder 51 moves in thesame direction as the travel direction of the wheeled carriage 23, whilefusing the wire W to fill the groove face S of the workpiece 22. Thewheeled carriage 23 moves synchronously with the movement of the welder51. During the movement of the wheeled carriage 23, the followerelements 44 turn and move, being in contact with the underside of theworkpiece 22 and welding operation is thus carried out with the weldbacking 11 being a specified distance kept away from the underside ofthe workpiece 22. When the workpiece detection sensor 46 detects thetrailing end of the workpiece 22, the air cylinder 40 is operated todraw the cylinder rod 40a and the follower elements 44 is allowed to beout of the contact with the workpiece 22. In such welding operation,since the backing lid portion 11b (more specifically, thecopper-aluminum alloy layer 16) of the weld backing 11, which directlycontacts the penetration bead RB, is cooled by cooling water, therebyspeeding up the solidification of the penetration bead RB maintained bysurface tension, not only can the abrasion resistance and adherenceresistance of the surface of the backing lid portion 11b be highlyimproved, but also damage to the weld backing 11b brought about by weldheat can be avoided.

FIG. 9 shows a section of the weld zone obtained by the full penetrationwelding.

As shown in the drawing, filler metal material M rises above the surfaceof the workpiece 22, forming a weld bead FB, while there is formed thepenetration bead RB on the underside of the workpiece 22, the bead RBbeing formed by the filler metal material M leaked through the root.After welding has been done, these weld bead FB and penetration bead RBare removed by grinding so that they become flush with the surface andrear face of the workpiece 22 respectively or they remain withoutundergoing such a finishing treatment.

Although the above description has been made taking the case for examplewhere full penetration welding is sequentially carried out with thewheeled carriage 23 moving from the leading end of the workpiece 22 toits trailing end, it is also possible to weld a local part of theworkpiece 22 by the use of the movable backing positioning system 21. Inthis case, it is possible to arrange such that the travel distance ofthe wheeled carriage 23 is calculated from the rotation speed of thewheels 24 detected by the rotary encoder 27, and according to thiscalculation, the wheeled carriage 23 automatically travels to a desiredweld position.

In this application example, the movable backing positioning system 21is provided with the wheeled carriage 23 of the mobile type, however,the driving method of the wheeled carriage 23 is not necessarily limitedto this. For example, the wheeled carriage 23 may be towed or pushed bythe use of a pinion and rack mechanism driven by an independentactuator.

Although the movable backing positioning system 21 of the aboveapplication example includes the arms 29 that are secured to the wheeledcarriage 23 with screws, the arms 29 may be attached to the wheeledcarriage 23 through air cylinders and after letting the wheeled carriage23 in the interior space of, for example, a box-shaped workpiece, thearms 29 may be extended by means of the air cylinders. The operation ofthe air cylinders can be controlled during the travel of the wheeledcarriage 23, and this makes it possible to adjust the position of theweld backing 11 to conform with the weld line, even if the weld line iscurved.

The construction of the cooling water chambers 12, 12a of the weldbacking 11 of this embodiment could be modified. A modification of theweld backing of this embodiment is shown in FIG. 10. According to themodification, there are provided a cooling water inlet 13a' and acooling water outlet 13b' at the right and left of the bottom of acooling water chamber 12'. At the center of the bottom of the coolingwater chamber 12' is disposed a weir 52. The provision of the weir 52prevents the direct flow of cooling water from the cooling water inlet13a' to the cooling water outlet 13b', which enhances the coolingeffects on the backing lid portion 11b' and, more particularly, thecopper-aluminum alloy layer 16'. The copper-aluminum alloy layer 16 iscooled by the circulation of cooling water in the above embodiment, butthe layer 16 could be cooled by liquid air or the like stored in thechamber.

Referring to FIGS. 11 to 13, a second application example of the weldbacking of the invention will be hereinafter described.

A movable backing positioning system 60 according to this example isapplied to the case of welding of a corner joint. The construction andfunction of the wheeled carriage 23 and other members of the secondapplication example are generally identical with those of the firstapplication example. Therefore, only the characteristic featuresinherent to the second application example will be described in thefollowing description. The parts that are substantially equivalent tothe parts of the first application example are indicated in the drawingsby the same numerals as used in the first application example and adetailed description on those parts will be omitted.

In the second application example, either one of the right and left arms29 which are screwed in the brackets 28 of the wheeled carriage 23 isshorter than the other, and the longer arm 29 is equipped with anauxiliary wheel 24a in the vicinity of the tip thereof for supportingthe arm 29. Disposed above the upper plate 23a of the wheeled carriage23 is a base 63 that can be freely lifted or lowered by a verticalmotion air cylinder 62 through front and back struts 61. A movablemember 65 is disposed at the center of the base 63. This movable member65 can be freely moved in a lateral direction (i.e., a directionperpendicular to the travel direction of the wheeled carriage 23) alonga guide member 64 fixed at the base 63, by means of a horizontal motionair cylinder (not shown). The movable member 65 includes, at one side,an inclined face 65a inclined at 45° with respect to the horizontalplane and guide rollers 66 and 67 at the upper end and a side. Theseguide rollers 66, 67 turn, being in contact with the upper wall and sidewall of the workpiece 22, respectively.

The inclined face 65a of the movable member 65 has a supporting plate 68fixedly attached thereto, which is longer in size than the movablemember 65 in a longitudinal direction. A backing retaining plate 69 isdisposed above and in parallel with the supporting plate 68. A weldbacking 71 is fixed on the top of the backing retaining plate 69 throughtwo pedestals 70 and the position of the weld backing 71 is adjustableby means of adjusting bolts 72. Fixed to the backing retaining plate 69are four struts 73 projecting towards the supporting plate 68. Eachstrut 73 extends downwards under the supporting plate 68, passingthrough an eye hole 74 formed on the supporting plate 68 and has aretaining ring 73a at the tip thereof. There are provided fourcompression springs 75 between the underside of the backing retainingplate 69 and the top of the supporting plate 68, each surrounding thestrut 73. By the provision of the compression springs 75, the weldbacking 71 is resiliently supported on the supporting plate 68. Thebacking retaining plate 69 is equipped with guide rollers 76 and 77 atits front and rear ends respectively. The guide rollers 76, 77 turn,being in contact with the upper wall and side wall of the workpiece 22respectively and function to maintain a predetermined spacing betweenthe weld backing 71 and the workpiece 22.

The weld backing 71 of this application example is substantiallypentagonal in section as shown in FIGS. 14(a) and 14(b), snugging in thecorner of the workpiece 22, and its tip portion opposite to theworkpiece 22 is chamfered. Although the weld backing 71 made from copperor a copper alloy according to the second application example could becomposed of a backing box-shaped body portion and a backing lid portionwhich are separately formed like the first application example, the weldbacking 71 described herein is formed as one unit and at least thesurfaces of the chamfered portion is covered with a copper-aluminumalloy layer 73 having the above-described composition in order to ensurehigh abrasion resistance and adherence resistance. Like the firstapplication example, the interior space of the weld backing 71 is acooling water chamber 79 communicating with a cooling water inlet 80 anda cooling water outlet 81.

According to the movable backing positioning system 60 of this example,by moving the wheeled carriage 23 along the weld line with the weldbacking 71 set in the corner of the workpiece 22, the guide rollers 30provided at the tip of the arms 29 are guided along the inner side wallsof the workpiece 22 and the guide rollers 66, 67, 76 and 77 are guidedalong the upper wall and side wall of the workpiece 22, so that thecorner joint of the workpiece 22 in the form of, for example, a box canbe continuously and easily welded.

The weld backing 71 mounted on the top face of the backing retainingplate 69 could be produced in other shapes, according to theconfiguration of the penetration bead requited. FIGS. 15(a) and 15(b)show a modification of the weld backing used in the second applicationexample. A weld backing 71' according to the modification is formed fromcopper or a copper alloy into a cylindrical shape in order to obtain arounded, smooth penetration bead. The peripheral face of the cylindricalweld backing 71' is covered with a copper-aluminum alloy layer 78',especially, at the position opposite to the workpiece 22. This weldbacking 71' is secured to inverted T shaped pedestals 70'. In FIG. 15,reference numeral 79' represents a cooling water chamber, 80' representsa cooling water inlet, and 81' represents a cooling water outlet.

The movable backing positioning system 60 of the second applicationexample can be possibly modified. For example, the arms 29 may be sodisposed as to be shrunk and stretched in relation to the wheeledcarriage 23, as described in the first application example.

Industrial Applicability

According to the invention, since the copper-aluminum alloy layer formedon the surface of the weld backing made from a material such as copperor a copper alloy has high abrasion resistance and high adherenceresistance due to the low affinity to the penetration bead, the surfaceof the weld backing can be kept smooth so that full penetration weldingcan be carried out without troublesome weld backing replacement. Theweld backing of the invention is suited for use in full penetrationwelding and suitably applicable to a movable backing positioning systemthat can be moved along the weld line of a workpiece.

Further, since the copper-aluminum alloy layer formed on the surface ofthe weld backing of the invention is cooled by a cooling means, thesolidification of the penetration bead maintained by surface tension isspeeded up. This brings about a further Improvement in the abrasionresistance and adherence resistance of the weld backing. Such a weldbacking enables it to perform welding operation for a long period andtherefore is particularly useful in the case of welding long workpieceswith a continuous welding apparatus.

We claim:
 1. A weld backing adapted to be held against the underside ofa workpiece to provide weld-metal support in full penetration welding,comprising: a substrate made from copper or a copper alloy; and acopper-aluminum alloy layer containing 9 to 23% by weight of aluminumand formed at least on the surface of the substrate which faces a weldzone.
 2. The weld backing as claimed in claim 1, wherein thecopper-aluminum alloy layer has a hardness of 250 to 700 mHv.
 3. Theweld backing as claimed in claim 1, wherein the copper-aluminum alloylayer contains aluminum preferably in the range of 16 to 22% by weight.4. The weld backing as in claim 1, wherein the copper-aluminum alloylayer has a thickness of 20 to 300 μm.
 5. The weld backing as claimed inclaim 1, further comprising cooling means for cooling thecopper-aluminum alloy layer.
 6. The weld backing as claimed in claim 5,wherein the cooling means is a cooling medium that is circulated orstored within an interior space defined in the weld backing.
 7. The weldbacking as claimed in claim 1, wherein the copper-aluminum alloy layercontains aluminum preferably in the range of 16 to 22% by weight and hascooling means for cooling the copper-aluminum alloy layer.
 8. The weldbacking as claimed in claim 1, which is made from copper or a copperalloy;wherein the copper-aluminum alloy layer is formed on the substratemade from copper or copper alloy; and wherein a cooling medium servingas the cooling means for cooling the copper-aluminum alloy layer iscirculated or stored within an interior space defined in the weldbacking.
 9. The weld backing as claimed in claim 1, comprising abox-shaped body portion which is open at one end and closed at the otherend so as to form a bottom and a lid portion for closing the opening endof the box-shaped body portion,wherein at least the lid portion is madefrom copper or a copper alloy and the copper-aluminum alloy layer isformed on the surface of the copper or copper alloy which forms the lidportion as the substrate, and wherein a cooling medium serving ascooling means for cooling the copper-aluminum alloy layer is circulatedor stored within an interior space defined by the box-shaped bodyportion and the lid portion.
 10. The weld backing as claimed in claim 8,wherein the cooling medium circulated within the interior space isintroduced into the interior space through an inlet formed at one sideof the interior space and let out through an outlet formed at the otherside, and wherein the inlet and outlet are formed as to be offset fromeach other.
 11. The weld backing as claimed in claim 8, wherein thecooling medium circulated within the interior space is introduced intothe interior space through an inlet and let out through an outlet, theinlet and outlet being formed at the same side of the interior space,with an weir between.
 12. The weld backing as claimed in claim 8, whichis substantially pentagonal or circular in section.
 13. The weld backingas claimed in claim 1, wherein the copper-aluminum alloy layer is formedby applying aluminum infiltration treatment to the surface of thesubstrate made from copper or a copper alloy.
 14. The weld backing asclaimed in claim 1 which is mounted on a movable backing positioningsystem comprising:(a) a wheeled carriage for movably supporting the weldbacking at the underside of the workpiece so as to face the weld backingto the workpiece towards the workpieces, the carriage being movablealong a weld line of the workpiece; (b) follower elements attached tothe weld backing, which follow along the movement of the underside ofthe workpiece, being in contact with the underside of the workpiece allthe time to maintain the gap between the underside of the workpiece andthe weld backing to be suitable for obtaining desired bead thickness;and (c) energizing means for energizing the weld backing such that thefollower elements are always in contact with the underside of theworkpiece.